Reoffending rates for young graduates of the Government's controversial boot camps are being kept secret on "privacy" grounds.

Almost $350,000 has been spent on the last-chance military-style activity camps (MAC) in the past two years, with four more planned for next year at a cost of $36,000 for each participant.

So far, the only information released has been about the two "concept camps" run at the end of 2010, which showed all but two of the 17 teens on the programme went on to reoffend. Requests for information about the 78 participants in the seven camps run since were refused by both the Ministry for Social Development and its Associate Minister Chester Borrows, who said making public the information about the "nature of offences or offending" could identify the youth involved.

When queried if this was because the crimes were high profile, such as homicide or rape, the minister declined to answer.

Labour MP Jacinda Ardern said it was not good enough to keep quiet on the results from more than two years of the programme.

"When these camps were established we pushed back against them as being universally panned for not having good outcomes. And now we still don't know if they're worthwhile or if the Government needs to take another look."

Ardern said other programmes were shut down to make way for the camps. "At that time they had no problem talking about results and those were even smaller numbers [of teens]. So I don't know why they're claiming they can't talk now."

Kate Stone, from the youth justice group JustSpeak, said better policy could not be made without proper information. "This is particularly relevant with respect to contentious policies such as ‘boot camps', which have a questionable evidential basis," she said. The MAC programme, which runs for nine weeks and is designed to cut reoffending among 15 to 17-year-olds, includes a wilderness camp, education and drills. They are held at Te Puna Wai youth residence near Christchurch as part of longer Youth Court "supervision with residence" orders after exhausting other sentencing options.

Data released by the ministry in July 2011 about the first two "concept camps" gave a reoffending rate of 88 per cent, compared to 79 per cent overall for teenagers given "supervision with residence orders" after five years.

Deputy chief executive of Child, Youth and Family, Bernadine MacKenzie, said more time was needed before the programme could be properly evaluated. She said the offending data was provided by police "in confidence".

Borrows refused to release reports on the programme because he was yet to consider them. He also withheld the information on privacy grounds. The Sunday Star-Times will complain to the ombudsman about the refusal.